Allylsilanes

Scheme 25 Allylsilanes from Trimethyl[2-(phenylsulfonyl)ethyl]silane [109,110]
SiMe 3
1. PhSH, AIBN
2. H2O2 O O
S
Ph
54
SiMe 3
1. BuLi
2. R1R2CO 3. MsCl
4. 6% Na/Hg
R1 ,R2 = (CH2) 3 95%
R1 ,R2 = (CH2) 4 94%
R1 = R2 = Ph 95%
R1 = H; R2 = Ph 92%
(2-Cyclopentylideneethyl)trimethylsilane [55,R 1 ,R 2 = (CH 2) 4]; Typical Procedure: [109]
1.6 M BuLi in hexane (40 mL, 64 mmol) was syringed slowly into a suspension of sulfone
54 (15 g, 62 mmol) in anhyd Et 2O (70 mL) at ±708C. The white suspension changed immediately
to a pale yellow soln. After the mixture had stirred for 25 min, cyclopentanone
(5.4 g, 62 mmol) was added. The soln was warmed to rt over 20 min, cooled to ±108C, and
MsCl (7.1 g, 62 mmol) in anhyd Et 2O (5 mL) was introduced. A white precipitate of LiCl
formed instantly. The suspension was refluxed for 25 min, cooled, diluted with Et 2O
(100 mL), washed with aq NaCl, dried (MgSO 4), filtered, and concentrated. The colorless
residue was dissolved without further purification in a mixture of MeOH (50 mL) and
Na 2HPO 4 (35.2 g, 0.25 mol). After the resulting suspension had been cooled to ca. 0 8C, 6%
Na/Hg amalgam (75 g) was added in small portions. The reductive elimination was completed
in 1 h. The suspension was diluted with Et 2O, decanted, and the solvent was removed
in vacuo. The residue was diluted with petroleum ether (bp 35±60 8C, 100 mL),
washed with H 2O, dried (MgSO 4), and passed through a short column (silica gel). Removal
of the solvents under reduced pressure gave the product; yield: 9.8 g (94%).
4.4.40.13 Method 13:
Formation of Exocyclic Allylsilanes by the Ramberg±Bäcklund Reaction
Six-membered exocyclic allylsilanes with a variety of substituents â to silicon have been
prepared bythe Ramberg±Bäcklund alkenation reaction of á-sulfonyl sulfones. [112] For example,
treatment of bis-sulfone 57 with butyllithium at ±788C, followed bywarming to
room temperature, yields allylsilane 58 (R 1 = H) (Scheme 26). [112] If the lithiated sulfone
from 57 is alkylated, and a second equivalent of butyllithium is added, â-substituted allylsilanes,
for example, 58 (R 1 = Me, Bn), maybe synthesized bythis protocol. Bis-sulfone 57
is available from cyclohexyl phenyl sulfone (56) bylithiation followed bysulfenylation
and oxidation with 3-chloroperoxybenzoic acid.
Scheme 26 Preparation of Exocyclic Allylsilanes by the Ramberg±Bäcklund Reaction [112]
O
O
Ph
S H
56
FOR PERSONAL USE ONLY
854 Science of Synthesis 4.4 Silicon Compounds
1. BuLi
2. Me3Si(CH2)2STs 3. MCPBA
O O O O
Ph
S S
57
SiMe3
1. BuLi, −78 oC 2. R1X, −78 to −20 oC 3. BuLi, −78 to 25 oC R 2
R 1
R 1
R1 = H 80% (step 1 only)
R1 = Me 69%
R1 = Bn 80% 58
Sarkar, T. K., SOS, (2002) 4, 837. 2002 Georg Thieme Verlag KG
55
SiMe 3
SiMe 3